1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a technique which can enhance the reliability of terminal portions of signal lines formed on a substrate.
2. Description of the Related Art
A liquid crystal display device sandwiches liquid crystal between two glass substrates consisting of a TFT substrate and a color filter substrate, and forms an image by controlling a quantity of light which passes through pixels in response to electric signals. With respect to the signals for forming the image, through terminal portions formed on the TFT substrate, scanning signals are supplied to scanning lines and image data signals are supplied to data signal lines. In response to the scanning signals, TFTs are selected and the TFT fetches the data signals thus controlling voltages of the respective pixels.
Generally, signals are supplied to the terminal portions from the outside via a flexible printed circuit board or the like. The scanning lines, data signal lines and the like are determined based on the resolution of a screen or intervals between pixels. On the other hand, the flexible printed circuit board is standardized, and intervals between terminals of the flexible printed circuit board are also standardized. Further, the intervals between terminals are standardized by also taking a condition on connection of the flexible printed circuit board with the glass substrate into consideration.
Accordingly, the intervals between terminals differ from intervals between scanning lines and intervals between data signal line and, in general, the intervals between terminals are set smaller than the intervals between scanning lines and the intervals between data signal lines. Due to such a constitution, a length of a connection portion which connects a terminal corresponding to a center portion of the flexible printed circuit board with the scanning line or the data signal line differs from a length of a connection portion which connects a terminal corresponding to a peripheral portion of the flexible printed circuit board with the scanning line or the data signal line. In this case, the resistance of the scanning line or the data signal line differs depending on a position of the scanning line, the data signal line or the like thus giving rise to a drawback that delay of a scanning signal or distortion of a data signal or the like differs depending on the position of the line.
JP-A-6-11721 (patent document 1) discloses a technique which makes the resistances of lines connecting the scanning lines or the like with the terminal portions equal to each other for eliminating the difference in resistance value depending on the position of the scanning line or the data signal line. That is, in the technique disclosed in patent document 1, for example, a width of a connection portion which connects a terminal portion corresponding to a center portion of a flexible printed circuit board and the scanning line or the like with each other is set smaller than a width of a connection portion which connects a terminal portion corresponding to a peripheral portion of the flexible printed circuit board and the scanning line or the like with each other.
On the other hand, to explain a liquid crystal display panel, a plurality of liquid crystal display panels is formed on a large-sized mother glass and, thereafter, by cutting the mother glass, individual liquid crystal display panels are formed. The cutting is performed by scribing or the like. When the glass is cut by scribing, glass debris is generated. When the glass debris adheres to the vicinity of the terminal and pressure is applied to the terminal from the outside, there exists a possibility that disconnection of a line occurs in the vicinity of the terminal. JP-A-9-90399 (patent document 2) discloses a technique which can prevent such disconnection of the line in the vicinity of the terminal due to a foreign material from the outside.
FIG. 7A and FIG. 7B are enlarged schematic views showing a portion in the vicinity of a terminal of a liquid crystal display panel. FIG. 7A is an enlarged plan view showing the vicinity of terminal portions 100, and FIG. 7B is a cross-sectional view taken along a line A-A in FIG. 7A. In FIG. 7A, a TFT substrate 10 and a color filter substrate 20 face each other in an opposed manner with a predetermined gap therebetween, and liquid crystal is sandwiched between the TFT substrate 10 and the color filter substrate 20. The liquid crystal is sealed by the TFT substrate 10, the color filter substrate 20 and a sealing portion 15.
In FIG. 7A, the terminal portions 100 which are connected with the flexible printed circuit board 30 are formed on an end portion of the TFT substrate 10 at fixed intervals. Assume that the terminal portions 100 shown in FIG. 7A are connected with scanning lines 11, as shown in FIG. 2A. Intervals between the scanning lines 11 formed in a display region of the liquid crystal display panel are set larger than intervals between the terminal portions 100 and hence, lines which extend from the periphery of the flexible printed circuit board 30 and are connected with the scanning lines 11 are spread outwardly, and lines which extend from a center portion of the flexible printed circuit board 30 and are connected with the scanning lines 11 extend in a straight manner. To set resistance values of the scanning lines 11 to a fixed value, the lines which are connected with the terminals arranged at the center portion of the flexible printed circuit board 30 are formed of a fine line, while the lines which are connected with the terminals arranged at the periphery of the flexible printed circuit board 30 are formed of a bold line.
Respective individual liquid crystal display panels are formed by cutting a large-sized mother glass. FIG. 7B is a cross-sectional view of the liquid crystal display panel showing such a situation. In FIG. 7B, the color filter substrate 20 is cut along a cutting line CFC, and the TFT substrate 10 is cut along a cutting line TFTC. Since the terminal portions 100 are formed on the TFT substrate 10, the TFT substrate 10 has an area larger than an area of the color filter substrate 20. Here, the cutting is performed by scribing or the like and hence, glass debris PG is generated.
When the glass debris PG is brought into contact with a specifically fine portion of the connection line 111 of the scanning line 11 and pressure is applied to such a portion from the outside, the connection line 111 is disconnected at such a portion. Due to such disconnection, one line in a display region becomes defective and hence, the whole liquid crystal display panel becomes defective. When such disconnection is generated before shipping a product from a factory, it is possible to prevent the defective product from being shipped to a market by the examination. However, there may be a case that the fine connection line 111 is half-disconnected, and when a half-disconnected portion is completely disconnected during the operation of the product in the market after shipping, the product becomes defective in use.
To prevent the occurrence of the disconnection of the connection line 111, patent document 2 discloses a technique which can reduce probability that the glass debris or the like is brought into contact with the terminal by forming a layer having the substantially same constitution as a color filter between the terminals and by forming a projecting portion on both sides of the terminal. However, the above-mentioned technique requires processing for forming the projecting portion between the terminals thus pushing up a manufacturing cost.
Further, the patent document 2 also discloses a technique which can increase a width of a line between the terminal portion 100 and the scanning line 11 in addition to the technique for forming the projecting portion between the terminal potion 100 and the scanning line 11. However, patent document 2 fails to disclose a technique which changes a line width of the connection line 111 between the terminal portion 100 and the scanning line 11 or the data signal line 12 for setting the resistances of the scanning lines 11 or the data signal lines 12 to a fixed value.
Here, in an attempt to apply the technique disclosed in the patent document 2 to a technique which changes the width of the connection line 111 for setting the resistances of the scanning lines 11 or the resistances of the data signal lines 12 to a fixed value, a drawback shown in FIG. 8 arises. FIG. 8 is a plan view substantially equal to FIG. 7A. In FIG. 8, at the center portion of the flexible printed circuit board 30, the scanning lines 11 which are shown in FIG. 2A, the connection lines 111 and the terminal portions 100 have the substantially same width. When the width of the connection line 111 corresponding to the periphery of the flexible printed circuit board 30 is increased for setting the resistances of the scanning lines 11 to a fixed value, as shown in FIG. 8, a distance d between the connection lines 111 is decreased thus giving rise to a possibility of a drawback that short-circuiting occurs between the connection lines 111.
To prevent such short-circuiting between the connection lines, as described in patent document 2, the projecting portion formed of the color filter or the like may be formed between the connection lines 111. However, such a technique pushes up a manufacturing cost. Further, the intervals between the terminals are fixed and hence, the width of the connection line 111 which corresponds to the periphery of the flexible printed circuit board 30 cannot be set to a fixed value or more and hence, it becomes practically impossible to set the resistances of the scanning lines 11 to a fixed value.